The corrosion of metallic parts and raw materials is a problem that is encountered by manufacturers, transportation companies, retailers and the consuming public alike. Unchecked corrosion can lead to a reduction in value or a diminishing of the lifespan for metallic items. While corrosion may come in many forms and may be the result of many different causes, it is the corrosion that results from the ambient environment within which a part or metallic item is stored or transported to which this invention is directed.
The most common metals which are susceptible to corrosion from ambient or atmospheric conditions are iron or ferrous compounds, aluminium, brass, copper, and lead. The corrosion of such metals, and metallic items created from them, may take the form of oxidation, tarnishing, pitting, discolouration or the mottling of the exterior surface. Traditionally, corrosion of this nature is associated with contact between the metallic surface and liquids, such as water or acidic compounds. However, in many instances the corrosion may be a direct result of the ambient atmospheric conditions within which the metallic item is situated. For example, metallic parts, machinery and raw materials are often exposed to gaseous compounds of oxygen, water vapour, carbon dioxide, nitrogen dioxide, sulphur dioxide and other such gases which can create an inherently corrosive environment. It is therefore imperative that steps be taken to prevent corrosion from exposure to such atmospheric elements, particularly during shipping and storage of metallic items. When such items are also subjected to sodium chloride (for example when shipped by sea or by truck in northern climates during the winter) even further precautionary steps need to be taken.
While a variety of methods and devices have been developed to reduce or help eliminate corrosion during storage and transportation, one of the most promising to date has been the development of vapour phase corrosion inhibitors. In general, vapour phase corrosion inhibitors release gaseous compounds which help to protect the surfaces of metals through the deposition of a protective film or coating on the corrodible surface. Provided that a sufficient supply of the vapour phase corrosion inhibitor is available, a metallic item can be protected for a considerable length of time.
In the shipping and transportation of metallic parts or materials, others have proposed various methods of presenting vapour phase corrosion inhibitors in sufficient supply to ensure a constant deposition onto the corrodible surface. Such devices and methods include the use of foam packing pellets or chips which have been injected with a liquid component that slowly evaporates to provide a constant supply of vapour phase corrosion inhibitor. Similarly, others have utilized solid components that sublimate into a vapour phase corrosion inhibitor. Still others have laminated a cellulose or similar layer to the underside of a tarpaulin or cover and saturated the cellulose layer with a liquid component that evaporates into a vapour phase corrosion inhibitor.
While all of these prior methods and devices have met with some degree of success, they all suffer from their own inherent limitations and difficulties. Utilizing solid or liquid compounds physically applied to the exterior surface of porous substrates and anticipating their rate of sublimation or evaporation into a vapour phase corrosion inhibitor can be difficult, particularly where atmospheric conditions such as temperature and pressure can vary and thereby affect the rate of sublimation and evaporation. The physical nature of the pores in the substrate and the degree of saturation also can affect the rate of release of vapour phase corrosion inhibitor thereby making it difficult to control the concentration of inhibitor surrounding a metallic item. Furthermore, in order to ensure that sufficient levels of solid or liquid corrosion inhibiting compounds are available, the substrates that have thus far been used have been soft and porous with little inherent strength or abrasion resistance. For example, in the case where a liquid corrosion inhibitor is sprayed onto a cellulose layer laminated to the underside of a tarpaulin, the cellulose layer may be subjected to abrasion which may result in an area having little or no corrosion protection. That is, should a portion of the cellulose layer be damaged or stripped off, a section or portion of the metallic item may not receive adequate protection.
Similarly, the use of impregnated foams or silica gels have limited application. To ensure that an adequate supply of the solid or liquid inhibiting compound is adjacent to the corrodible surface, the entire metallic part or component must normally be encapsulated within the foam or silica gel. In addition, the use of impregnated foam or silica gel does not provide protection from the elements of weather, from ultra violet radiation from the sun, nor do they provide a barrier to dust and dirt.